<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    body,ul {
        list-style: none;
        padding: 0;
        margin: 0;
    }

    ul li {
        background: #000;
    }

    ul li p {
        padding: 10px;
        margin: 0;
        color: #fff;
    }

    /* 关键代码 */
    .test-1 ul {
        display: flex;
    }

    .test-1 li {
        box-sizing: content-box;
        width: 33.3%;
        text-align: center;
        border: 1px solid red;
    }
</style>
<body>
    <div id="app"></div>
    <div class="test-1">
        <ul>
            <li>
                <p>
                    床前明月光，疑是地上霜，举头望明月，低头思故乡
                </p>
            </li>
            <li>
                <p>
                    床前明月光，疑是地上霜，举头望明月，低头思故乡
                </p>
            </li>
            <li>
                <p>
                    床前明月光，疑是地上霜，举头望明月，低头思故乡
                </p>
            </li>
        </ul>
    </div>
</body>
</html>